Sunday, December 03, 2006

The "disillusionment" consists mainly of two recently published books, one by Peter Woit and the other by Lee Smolin.

An email interview with Sunil Mukhi of the Theoretical Physics group at the Tata Institute of Fundamental Research (TIFR), Mumbai.

What do you make of the recent disillusionment with string theory? They seem to feel let down that it (the string theory) has led them u the garden path,, as it were, and that it reall led nowhere. Is this an overreaction? Or, is it coming from those who did not subscribe to string theory from the beginning?

The "disillusionment" consists mainly of two recently published books, one by Peter Woit and the other by Lee Smolin. I don't believe either of these authors has ever particularly subscribed to string theory, indeed they have been somewhat negative about it for a long time.

It is more than 20 years since string theory emerged. Do you think it is going places, and is able to throw light on things uneplained till now?

It is definitely able to throw light on things unexplained till now. From experiments we know that in nature there are two types of forces, "gauge" forces and gravitational forces. String theory is the only framework in which the two are naturally unified. It potentially holds the answer to "why" type questions - why are the fundamental forces the way they are, why is the spectrum of observed particles the way it is, why are the interactions among particles what they are. It has not provided a definitive answer to these questions, but I'm not aware of any other approach that even holds the promise of doing so.

It's important to realise that not every physicist is interested in these "why" questions. Some people are more interested in "how" and "what" questions: how do materials superconduct, what are the properties of a crystal etc. These are scientifically valid, important and in some ways more practical questions, and string theory does not address these.

The most critical view of string theory is that it has not yet found experimental verification? Is this an unfair demand?

It is a perfectly fair demand. String theorists have been looking for ways to experimentally test the theory. There are many levels of verification - for example string theory naturally incorporates a new symmetry called supersymmetry, and supersymmetry will be tested at the Large Hadron Collider in Geneva starting next year. String theory also provides possible scenarios for the cosmological evolution of the universe and these too could be tested in the future.

I would like to emphasize that it is the questions being asked that make this subject hard to test, rather than the answers proposed by string theory. Any proposal to unify fundamental forces or explain the early universe involves incredibly high energy scales and will therefore be extremely difficult to test.

Is string theory creating waves among the Indian theoretical physicists?

Yes. I think there is considerable interest in the subject in India. We have had many successful String conferences here, the largest being "Strings 2001" which featured distinguished scientists like Nobel Laureate David Gross as well as Stephen Hawking and Edward Witten. The press and public were also intrigued by the questions that this subject tries to address.

Have there been any interesting contributions from the Indian side?

Many fundamental contributions have been made by Indians working in India. In the last ten years it has become clear that "duality" is a basic property of string theory and provides a powerful method to understand the subject. Indian physicists have written many papers about duality, including some of the pioneering ones. The physics of black holes has undergone a revolution through the use of string theory. This too involved crucially the work of Indian physicists, and continues to do so today. Finally, the most popular scenario for describing a universe with a cosmological constant is jointly authored by an Indian physicist along with three physicists at Stanford.

Is the anger with the supposed failure of string theory a short-lived one? Or, is it something more serious, which would calls for a critical reassessment of string theory?

We are constantly engaged in critical assessments of the theory. I don't really know why two books written for a lay audience would change anything. The only thing that would change the situation would be a new idea to address the "why" questions, and for the moment there is no sign of that.

The public might well feel angered that string theorists have not answered the big "why" questions in two decades, but they need to realise that the questions are important and difficult, and 20 years might not be enough time to solve them.

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